The present invention relates to the art of earth boring and, more particularly, to a rotary rock bit with improved means for sealing the bearings from materials in the borehole. The present invention is especially adapted for use in that type of rotary rock bit popularly known as a three-cone bit; however, its use is not restricted thereto, and the present invention can be used in other types of rotary rock bits.
A three-cone rotary rock bit is adapted to be connected as the lowest member of a rotary drill string. As the drill string is rotated, the bit disintegrates the earth formations to form an earth borehole. The three-cone rotary rock bit includes three individual arms that extend angularly downward from the main body of the bit. The lower end of each arm is shaped to form a spindle or bearing pin. a cone A is mounted upon each bearing pin and adapted to rotate thereon. Individual bearing systems promote rotation of the cone cutters. The bearing systems have traditionally been roller bearings, ball bearings, friction bearings, or a combination of the aforementioned bearings. The cone cutters include cutting structure on their outer surfaces that serve to disintegrate the formations as the bit is rotated. Various forms of seals have been provided between the cone cutter and the arms upon which they are mounted; however, the prior art seals have in many instances proven to be less than satisfactory.
The rotary rock bit must operate under very severe conditions, and the size and geometry of the bit is restricted by the operating characteristics. At the same time, the economics of petroleum production demand a longer lifetime and improved performance from the bit. In attempting to provide an improved bit, new and improved materials have been developed for the cutting structure of the cones. They have provided a longer useful lifetime for the cones. This has resulted in the bearing system of the bit being generally the first to fail during the drilling operation. Consequently, a need exists for improved bearing systems to extend the useful lifetime of the bit. In attempting to improve the bearing system, various seal systems have been provided to maintain the bearing area free of harmful materials. In attempting to provide an improved bearing system incorporating an improved sealing system, great care should be taken that the overall capacity of the bearing system is not reduced.
One problem encountered when trying to develop a satisfactory sealing system for the bit bearings arises due to the nature and extent of cone movement relative to the bearing shaft or pin. Good movement is complex and includes rapid axial and radial as well as wobbling motions. In lubricated sealed bearing bits, such motions generate pressure variations in the lubricant that are sensed by the seal means. Moreover, these sensed pressure variations often result in lubricant loss. Preferably, seal means for lubricated drill bit bearings should have the ability to withstand substantial pressure variations; the ability to seal effectively for long periods of time in the presence of sand or other foreign particles; and the ability to seal protectively in the face of excessive cone movement and wear. In air cooled bits wherein a gaseous fluid is circulated through the bit with some of the circulating fluid directed through the bit bearings for cooling and flushing of the bearing components, conditions often exist where the air pressure and volume is inadequate for optimum flushing of the bearings. Under these conditions, the cuttings generated by the bit action on the bottom cannot be efficiently lifted off the bottom of the borehole and tend to fall back to the bottom until a time when regrinding by the bit reduces the individual particles to a size small enough to be lifted by the low volume of circulating fluid. It can readily be appreciated that a bit working in a deep bed of cuttings with an insufficiency of fluid flushing through the bit bearings will be subjected to said cuttings filtering into the bearings unless a satisfactory sealing system is provided. In the bearings, the cuttings will be caught up between the rotating bearing members creating an abrasive grinding-milling-wearing action, which is extremely detrimental to the entire bearing cluster and can be a major factor in reducing bit bearing life.
The present invention provides a seal means which will act as a barrier to the pulverized cuttings, keeping these cuttings and other materials in the borehole from entering the bearing are through the cone mouth opening, thus providing a clean environment for the metal bearing elements and eliminating abrasive wearing action. This will vastly improve the bearing life by preventing abrasive cuttings from entering the bearings and contributing to wear of the individual bearing components, thereby contributing to the ultimate failure of the full bearing cluster. The shirttail of the bit body and the base of the cone cutter cooperate to retard materials in the borehole from contacting the seal means. Abrasive wear is considered a major factor in limiting bearing life in blast hole drilling bit applications and is especially significant in conditions where the air volume is marginal. This latter condition exists when air compressor equipment has been neglected and does not perform up to its rated capacity, or as is common with the smaller blast hole drills, the air volume rating of the compressor is marginal to start with. In lubricated sealed bearing bits, the improved seal will maintain the lubricant within the bearing area. The improved seal is provided without reducing the bearing capacity of the bit.